This application relates to hard disc drives and more particularly to an apparatus and method for controlling a lapping process, so as to create a read/write head that contains a primary magnetoresistive read element with a desired stripe height.
The storage medium for a disc drive is a flat, circular disc capable of retaining localized magnetic fields. The data that are stored upon the disc find physical representation through these localized magnetic fields. The data are arranged on the disc in concentric, circular paths known as tracks.
The localized magnetic fields can be detected by a magnetically sensitive head when they are brought in close proximity to the head. During operation, the disc continually rotates, meaning that for each rotation, a head fixed a given radius from the center of the disc would encounter every localized magnetic field along a given track.
A read/write head 100 capable of reading and writing localized magnetic fields upon the surface of a disc is depicted in FIG. 1. The read/write head 100 depicted in FIG. 1 is constructed from a body 102 composed of AlTiC (Aluminum, Titanium and Carbide) wafer material. Conjoined to the body 102 is a magnetoresistive read element and a write element, shown jointly as 104. The resistance of the magnetoresistive read element 104 changes when introduced to a magnetic field. Generally, the greater the magnetic field in which the magnetoresistive read element 104 is immersed, the higher its resistance. Accordingly, the magnetoresistive read element 104 is used to detect a localized magnetic field stored on the surface of the disc by orienting the localized magnetic field under the read element 104 and observing a change in the element""s 104 resistance.
To detect a change in the resistance of the read element 104, a constant current is passed through the magnetoresistive read element 104 and the voltage across the element 104 is observed. As the resistance of the element 104 increases due to the influence of a proximate magnetic field, the voltage across the element 104 increases proportionately. Thus, the change in resistance is observed as a corresponding rise in voltage across the read element 104. The constant current used to detect the localized magnetic fields is propagated through conductors 106, 108, which electrically contact opposite ends of the magnetoresistive element 104. The conductors 106, 108 run to a pair of wire bonds 110, 112, which join the conductors 106, 108 to a pair of elongated conductors 114, 116 that extend the length of the head 100, and join to detection circuitry (not pictured). The read/write head 100 also contains conductors 118, 120 through which a current is passed to record a magnetic field upon the surface of the disc. Conductors 118, 120 also run to a pair of wire bonds 122, 124, which join the conductors 118, 120 to a pair of elongated conductors 126, 128 that extend the length of the head 100, and join to writing circuitry (not pictured).
FIG. 2 shows a magnified view of a magnetoresistive read element 104. As can be seen from FIG. 2, the bottom edge 200 of the magnetoresistive read element 104 extends to the air bearing surface of the slider. The air bearing surface functions to create a xe2x80x9ccushionxe2x80x9d of air upon which the read/write head 100 floats as it is positioned over a rotating disc.
The top edge of the magnetoresistive read element 104 is identified by reference numeral 204. The distance between the bottom edge 200 and the top edge 204 of the magnetoresistive read element 104 is referred to as the xe2x80x9cstripe height.xe2x80x9d The stripe height of a magnetoresistive read element is an important variable, as it determines the sensitivity of the magnetoresistive element to a magnetic field. Generally, the shorter the stripe height, the more sensitive the magnetoresistive element, and vice versa.
As shown by FIG. 3, prior to processing, a magnetoresistive read element 104 has a stripe height on the order of 100,000 xc3x85. The conductors 106, 108 have approximately the same height. During manufacture, the magnetoresistive head is xe2x80x9clapped,xe2x80x9d thereby reducing the magnetoresistive read element""s 104 stripe height to that which is shown in FIG. 2, on the order of 500 xc3x85 (with a typical tolerance of xc2x110%), depending upon product requirements. xe2x80x9cLappingxe2x80x9d is a term used to describe a grinding process in which the magnetoresistive read element 104 and its associated conductors 106, 108 are literally ground down by an abrasive slurry, until the desired stripe height is achieved. The purpose of the lapping process is to reduce the stripe height of the magnetoresistive read element until the proper magnetic sensitivity has been created.
Ideally, it would be possible to directly test the sensitivity of the magnetoresistive read element during lapping, so that when the proper sensitivity had been achieved, lapping could be ceased. Unfortunately, by passing an electrical signal through the magnetoresistive read element, as is necessary in order to directly test the read element""s resistance, the likelihood of an electrostatic discharge between the magnetoresistive read element and the abrasive slurry is enhanced. Such an electrostatic discharge is harmful to the read element, and it is therefore desirable to minimize the likelihood of such a discharge.
It is known in the art that, during lapping, the resistance of a secondary resistive element can be monitored and used as a proxy for directly measuring the stripe height of a primary magnetoresistive element. When the resistance of the secondary magnetoresistive element reaches a predetermined level, it can be assumed that the stripe height of the primary magnetoresistive element is in its appropriate range, and lapping can be ceased. In order to use such a measurement-by-proxy scheme, the primary and secondary elements should be arranged so that there exists a known relationship between the sensitivity of the primary and secondary elements.
FIG. 4 shows an undiced, untapped wafer 400 containing two read/write heads 402, 404 and a lapping guide 406. Read/write head 402 contains a primary magnetoresistive element 408, and lapping guide 406 contains a secondary resistive element 410, the resistance of which is in known relation to magnetoresistive element 408. During lapping, the resistance of the secondary resistive element 410 is monitored. When the resistance of the secondary resistive element 410 reaches a certain level, it is assumed that the stripe height of the primary magnetoresistive element 408 is in its appropriate range, and lapping is ceased. To ensure that the resistance of the secondary resistive element 410 is in known relation to the stripe hieght of the primary magnetoresistive element 408, the top edges of the primary and secondary elements are aligned. Therefore, during lapping, the stripe height of the primary and secondary elements should be equivalent, and the resistance of the secondary element should serve as a suitable proxy for the stripe height of the primary element. This solution, which is known in the art, has problems, however. The distance between the primary and secondary elements 408, 410 is relatively great (perhaps 500 microns). Because of this great distance, the alignment of the top edges of the primary 408 and secondary elements 410 necessarily has a wide tolerance. Such a wide tolerance is undesirable, because it detracts from the accuracy with which the secondary resistive element 410 indicates the stripe height of the primary element 408. Thus, the secondary resistive element 410 is an unreliable proxy for the primary magnetoresistive element 408. Accordingly there exists a need for a means for accurately measuring and controlling the stripe height of a primary magnetoresistive element without subjecting the element to the risk of damage from electrostatic discharge.
The method and apparatus in accordance with the present invention solves the aforementioned problems and other problems by an apparatus or method as presented herein. The method involves grounding a primary magnetoresistive read element located on the read/write head to be lapped. Next, a test signal is passed through a secondary magnetoresistive read element that is also located on the read/write head. Lapping of the primary and secondary magnetoresistive elements is commenced. The lapping is continued until the test signal exhibits a desired characteristic.
Another aspect of the invention includes a read/write head with a primary magnetoresistive read element (used for reading data during operation of the disc drive into which the read/write head is palced). The read/write head also includes a secondary magnetoresistive read element, dimensioned in proportion to the primary magnetoresistive read element and positioned in proximity thereto.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.